Currently, an industrial robot is often used as a component assembly device that performs component assembly and so on. In an industrial robot that performs component assembly, an end effector, such as a hand, is provided at the end of the robot's arm for performing operations, such as gripping and pushing a component or a workpiece, to thereby perform component assembly.
Operations of a robot are generally controlled in accordance with position control. Therefore, in a case where a pre-programmed position of a component is different from the actual position of the component, contact between the component and another component or between the component and a workpiece produces a large force, which causes scratches or damage to the component.
As a measure against such a problem, a jig (namely, “buffer”) that absorbs the force produced due to the error in the position of the component may be separately installed. The buffer is required to have different properties depending on the form or material of the component. Therefore, different buffers need to be prepared for the number of types of components and to be individually designed, which is a disadvantage in terms of cost. Further, the apparatus becomes large, which is a problem.
There may be a case where a force sensor is installed between a robot and a hand and, when an excessive force is almost produced upon contact, the result of sensing by the force sensor is fed back for position control of the robot to thereby prevent the excessive force from being produced. In this case, a buffer is not necessary; however, the force sensor is expensive, which is a problem.
Further, an existing component assembly device constituted by a single robot has a problem, that is, has difficulty in reducing the work time for the following reasons. A force produced upon contact is the sum of an impact force arising from inertia and a force produced by the robot upon contact. The impact force arising from inertia is proportional to the product of the weight of the component and the movable part of the robot and the movement speed. In general, a robot has a large and heavy mechanism, and therefore, the movement speed immediately before contact needs to be decreased to reduce the impact force arising from inertia.
In the case where the force sensor is installed in the robot, an excessive force produced upon contact is sensed and the operation is stopped. However, the robot having a large and heavy movable part and a deceleration mechanism with a backlash is unable to make a sudden stop, and therefore, it is difficult to accelerate a response of force control. Accordingly, in order to reduce a force applied to the component upon contact, the speed at which the component is brought closer needs to be further decreased. As a result, the work time becomes long, which is a problem.
Some component assembly devices, such as “mounters”, are capable of performing faster assembly. However, mounters are dedicated machines specializing in fast mounting of small and light components, are not usable in assembly of components other than small and light components, and are relatively expensive apparatuses.
A robot can be used as a component assembly device to thereby increase versatility; however, the above-described problems exist.